The present invention relates to lasers and, more particularly, to the optics of a laser system for use in marking and coding applications.
Lasers suitable for use in such applications have been described in U.S. Pat. No. 4,618,961, U.S. Pat. No. 4,891,819 and U.S. Pat. No. 5,095,490. Additionally, in U.S. Pat. No. 4,652,722 there is described a laser apparatus utilising a plurality of coherent laser beams in conjunction with fixed reflecting means, beam tubes and a focusing lens, to providing marking indicia or permanent alteration of substrate surfaces. Claim 1 of U.S. Pat. No. 4,652,722 is directed to features which enable the optical path to be shortened and the specification describes how the optical path can be shortened using the reflecting means.
One of the main problems in building a compact and commercially viable laser marking system utilising multiple laser channels, is to position the laser channels in such a manner as to reduce the physical size of the channel assembly whilst simultaneously simplifying the optical configuration necessary to provide the required optical marking characteristics. In general, the physical size of individual lasers does not readily allow one to obtain simultaneously the optical spacing and angular relationships between the laser required for optimum optical performance. In U.S. Pat. No. 4,652,722 the inventors teach that one possible solution to this problem is to place the lasers in a near-parallel orientation and then re-direct each beam optically to both shorten the optical paths and to set the desired angular relationship between the individual laser beams.
However, the above patent specification does not deal with the problem of providing a suitably small character size from multiple dots.
U.S. Pat. No. 5,168,401 and-WO-A-9604584 describe optical systems which relate to the collimation of individual laser beams from laser diodes, but do not address the problems to which the present invention relates. EP-A-0538044 discloses a system similar in nature to U.S. Pat. No. 4,652,722 and U.S. Pat. No. 5,389,771 discloses an apparatus for folding a single beam emitted from a point source. None of these specifications is considered to be of particular relevance to the present invention. Also, WO8912369 discloses a multi-beam laser system.
According to the present invention, a laser apparatus comprises a plurality of individual lasers, each of the lasers having an output end from which a laser beam is emitted, and the lasers being mounted at angles to one another whereby their beams cross, wherein said laser output ends are disposed closely adjacent to one another; and a plurality of laser beam redirectors are disposed to intercept the laser beams emitted from the laser output ends, said laser beam redirectors being disposed to extend the length of the laser beam paths and decrease the angle between said laser beams, said laser beam redirectors being located between the laser output ends and a crossing point at which the beams cross.
By this means the resulting optical system can produce a plurality of marks properly spaced to produce alpha-numeric, graphic and/or machine-readable marks on moving substrates whilst providing a very compact system which can be fitted in relatively small spaces typically provided on production lines and the like.
The laser beam redirectors are preferably mirrors or refractive optical prisms.
Steering mirrors could be added to the beam paths to vary the angles between the laser beams, being steerable by electrical signals as desired.
A lens may be provided to focus the laser beams on to the target, the lens being preferably located between the point at which the laser beams cross and the target surfaces at a distance f from the crossing point which is the focal length of the lens.
According to the present invention, there may also be provided a laser beam splitting device for directing the laser beams to a plurality of targets, and the respective path lengths of the laser beams between the laser beam redirectors and each of the lenses, preferably provided as above for each of the targets, are preferably equal.